Commercial food preparation operations typically involve cooking, drying and/or browning of items. It is often necessary to apply these processes to large quantities of food articles in the shortest possible time, and this has lead to the use of continuous feed microwave ovens of several types.
One such microwave oven makes use of an elongated, single mode microwave energy applicator. The single mode applicator is designed from an electromagnetic standpoint to be a waveguide that applies microwave energy in a shape that is optimized depending upon the shape of the product being cooked. For example, if the product being cooked is relatively square in cross-section, the applicator may itself be designed as an elongated, tapered rectangular cavity that is several feet long.
Such an applicator is, by necessity, left open on both ends so that food articles to be cooked may travel on a conveyor which travels inside the waveguide. With food portion sizes appropriate for heating using an applicator of this design, the product entrance and exit may be constructed using well known techniques to prevent microwave leakage. For example, the entrance and exit openings are typically limited in size to be something less than the propagating waveguide dimension, which in turn depends upon the wavelength of the microwave energy. Thus, for microwave applicators designed for operating in the 900 Megahertz (MHz) region, as long as openings are no more than about 6 inches or so in each dimension, energy will be contained.
However, the small dimensions necessary in construction of such an applicator pose several problems.
First, there is no direct access available to the interior of the rectangular waveguide for easy cleaning. While such applicators have been assembled from component pieces, and typically bolted together, disassembly of such a unit can be quite time consuming. Since there can be no uninterrupted opening of more than about six inches, bolts or other fasteners are typically placed at a spacing which is no longer than that.
Second, it is often preferred that a so-called endless conveyor belt be used that has no breaks in it. However, there is typically no easy way of removing an endless conveyor belt from such an applicator, since this again requires disassembly of the applicator via removal of the fasteners.
A third difficulty arises from the fact that there must be sufficient clearance between the edges of the belt and the interior walls of the applicator so that the belt may freely run along. However, there is a tendency for small food particles to fall between the belt edges and the applicator wall. This causes additional maintenance problems, further exacerbated by the difficulty in obtaining access to the interior of the applicator in the first place, and then having to remove the belt to clean out these small food particles.